Diamond Cats is about an idol group of the same name, made up of three members; Atsushi, Rio and Yuuki. The manga revolves around the relationship between Yuuki and Rio. It's very graphic and full of smut.
In the second volume, the Diamond Cats series ends halfway and there are two other short stories. The first is about a boy named Shiki who is in love with his long-time friend, Yuuka. The second story is about a boy in the hospital named Hiroshi, who is constantly pursued by another patient in the hospital, Kiichi. No matter what happens Kiichi keeps coming back to win his love.